The present invention relates to the installation of hollow fittings in vessels, especially vessels used to contain flammable substances.
Certain industrial facilities require the storage of large quantities of chemicals, which is typically done by the use of large cylindrical vessels arranged adjacent one another in a storage area, i.e., a so-called tank farm. On occasion, one or more of the vessels may need to have an additional opening formed in a cylindrical side wall, a domed top wall, or a domed bottom wall of the vessel, e.g., for venting purposes. Typically, this is done by torch cutting a hole in the wall and then electric arc welding a hollow fitting in the hole. The hollow fitting typically includes a flanged end to enable external connectors to be connected thereto.
Special concerns exist in cases where the vessels are used to store highly flammable materials, because sparks generated by welding could generate an explosion. Even though the vessel to be modified is first emptied and cleaned, a spark could still ignite adjacent vessels. It would be highly time consuming and expensive to empty every vessel, however.
Conventional torch cutting and electric arc welding methods create a substantial ignition source which could ignite a fire or explosion when performed near vessels that store highly flammable materials.
Hole-cutting procedures are known which are flameless and sparkless, e.g., abrasive water jet cutting, and which could be used to cut a hole in a vessel, but the subsequent attachment of the hollow fitting in the hole by electric arc welding would create a dangerous ignition source.
Also, hollow fittings are known, such as the bulkhead fitting 10 shown in FIG. 1, which are used on flat plates, and can be attached to a hole in a plate by an all-screwed construction which eliminates the need for electric arc welding. The bulkhead fitting 10 is inserted through a hole in the flat plate 12 and is secured by a main nut 14 which threads onto the outside of a body barrel 16 of the bulkhead fitting. The interior of the body barrel 16 has a screw thread (not shown) to receive an external connector 17. A gasket 18 is compressed between the plate 12 and a body flange 20 of the bulkhead fitting 10 to create a pressure-tight seal around the hole. Aside from the fact that the bulkhead fitting 10 is not capable of being attached to a curved vessel wall, two other problems occur that make large bulkhead fittings 10 such as three-inch in diameter, or larger, unsuitable for most industrial applications.
The primary problem with large bulkhead fittings 10 is that the main nut 14 cannot be tightened sufficiently to produce the large force need to compress typical industrial gaskets. The main nut 14 wastes most of the tightening torque in overcoming the friction force between the face of the main nut 14 and the surface of the vessel wall 12. For example a six-inch diameter bulkhead fitting would require an eight-foot long wrench with a force of about sixteen hundred pounds applied to the end thereof to adequately compress a typical industrial gasket. Of course tightening conditions in this example are substantially impractical for industrial use.
Because of the problem with tightening the main nut 14, bulkhead fittings 10 are commercially available mostly for rubber gaskets, and smaller sizes about four inches in diameter and smaller. Bulkhead fittings are unsuitable for most industrial applications because rubber gaskets have limitations of temperature and chemical resistance. Typical industrial gaskets made from compressed fiber sheet or spiral windings will not work with large bulkhead fittings because the minimum sealing stress for such industrial gaskets is about ten times higher than the sealing stress required for rubber gaskets.
A secondary problem associated with large bulkhead fittings 10 is that it is relatively difficult to hold the body barrel 16 against rotation while tightening the main nut 14.
Accordingly, it would be desirable to enable a hollow fitting to be attached to a vessel wall in a pressure-tight manner without the need for spark producing methods such as torch cutting or electric arc welding.
It would also be desirable to enable a hollow fitting to be attached to a vessel wall in a pressure-tight manner using small, easily manipulated wrenches.
It would be further desirable to enable a hollow fitting to be attached to a vessel wall in a pressure-tight manner without having to hold the body barrel against rotation.
One aspect of the present invention relates to a method of installing a hollow fitting assembly with a pressure-tight seal in a hole disposed in a wall of a vessel. The method comprises the steps of:
A) inserting a hollow body element through the hole from a first side of the wall such that a free end of a body barrel portion of the hollow body element protrudes from a second side of the wall, and a body flange portion of the hollow body element bears against the first side, with a seal ring interposed between the body flange portion and the first side, the seal ring extending around the hole to form a pressure-tight seal;
B) inserting a force-distributing washer over the free end of the body barrel portion such that a first face of the washer faces toward the hole, and a second face of the washer faces away from the hole;
C) inserting a pusher flange onto the free end of the body barrel portion and attaching the pusher flange to the body barrel;
D) screwing jack bolts within internally threaded apertures formed in the pusher flange, causing free ends of the jack bolts to abut the second face of the force-distributing washer to push the first face of the washer toward the second side of the wall, and pull the body flange portion toward the first side of the wall for compressing the seal ring to form a pressure tight seal around the hole; and
E) attaching an external member to the body barrel portion.
Another aspect of the present invention relates to a vessel which includes a wall having a hole formed therethrough, and a hollow fitting assembly installed with a pressure-tight seal in the hole. The hollow fitting assembly comprises a hollow body element which includes a body flange portion bearing against a first side of the wall, with a seal ring disposed between the body flange portion and the first side. The seal ring extends around the hole to form a pressure-tight seal. The hollow body element further includes a hollow body barrel portion extending through the hole from the body flange portion. A pusher flange is attached to the body barrel portion. A force-distributing washer is disposed between the pusher flange and the second side of the wall, with a first face of the washer facing the second side, and a second face of the washer facing away from the second side. Jack bolts are threadedly secured within internally threaded apertures of the pusher flange, with free ends of the jack bolts pushing the force-distributing washer against the second side, and with threaded portions of the jack bolts forcing the pusher flange away from the vessel to pull the body flange portion toward the first side for compressing the seal ring to create a pressure-tight seal around the hole.